BUG: mistake dim 2 for cropping in segment_graymatter
BUG: mistake dim 2 for cropping in segment_graymatter

Former-commit-id: f6b90a72383767e01571f2b28d8ff634c86ef3f5
Former-commit-id: 101d27d42652629c4a6ae48404bbb9da54b43b0f
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox